Showing papers by "Tokyo University of Science published in 2001"

Selective Preparation of Monoclinic and Tetragonal BiVO4 with Scheelite Structure and Their Photocatalytic Properties

Abstract: BiVO4 powder with scheelite structure was obtained by hydrolyzing a nitric acid solution of Bi(NO3)3 and Na3VO4 with bases (Na2CO3 and NaHCO3) at room temperature. Tetragonal BiVO4 of a high-temperature form was obtained after 4.5 h of preparation time while monoclinic BiVO4 was done after 46 h. Although the structure and the band gap of tetragonal BiVO4 with scheelite structure were similar to those of monoclinic BiVO4, the photocatalytic activity of the tetragonal BiVO4 for O2 evolution from an aqueous AgNO3 solution under visible light irradiation was negligible. In contrast, the monoclinic BiVO4 showed high photocatalytic activity. Distortion of a Bi−O polyhedron by a 6s2 lone pair of Bi3+ plays an important role for high photocatalytic activity of the monoclinic BiVO4 under visible light irradiation.

Water Splitting into H2 and O2 on Alkali Tantalate Photocatalysts ATaO3 (A = Li, Na, and K)

Abstract: Alkali tantalate ATaO3 (A = Li, Na, and K) photocatalysts with perovskite-like structure showed activities for water splitting into H2 and O2 under UV irradiation. When the alkali tantalates were prepared in the presence of excess alkali, their activities were increased by 1 to 2 orders of magnitude. Scanning electron microscopy and photoluminescence measurements indicated that the excess alkali in the preparation increased the crystal size of NaTaO3 formed and prevented formation of alkali defects in NaTaO3 powder by volatilization, resulting in an increase in the photocatalytic activity. A LiTaO3 photocatalyst showed the highest activity among the naked alkali tantalate photocatalysts prepared in the presence of excess alkali. On the other hand, the activity of a NaTaO3 photocatalyst was increased by 1 order of magnitude when a NiO cocatalyst was loaded. The NiO(0.05 wt %)/NaTaO3 photocatalyst produced H2 and O2 from pure water with rates of 3.39 and 1.58 mmol h-1, respectively. The apparent quantum yie...

Quantitative and Reversible Lectin-Induced Association of Gold Nanoparticles Modified with α-Lactosyl-ω-mercapto-poly(ethylene glycol)

Abstract: Gold nanoparticles (1−10 nm size range) were prepared with an appreciably narrow size distribution by in situ reduction of HAuCl4 in the presence of heterobifunctional poly(ethylene glycol) (PEG) derivatives containing both mercapto and acetal groups (α-acetal-ω-mercapto-PEG). The α-acetal-PEG layers formed on gold nanoparticles impart appreciable stability to the nanoparticles in aqueous solutions with elevated ionic strength and also in serum-containing medium. The PEG acetal terminal group was converted to aldehyde by gentle acid treatment, followed by the reaction with p-aminophenyl-β-d- lactopyranoside (Lac) in the presence of (CH3)2NHBH3. Lac-conjugated gold nanoparticles exhibited selective aggregation when exposed to Recinus communis agglutinin (RCA120), a bivalent lectin specifically recognizing the β-d-galactose residue, inducing significant changes in the absorption spectrum with concomitant visible color change from pinkish-red to purple. Aggregation of the Lac-functionalized gold nanoparticle...

Self-assembly of poly(ethylene glycol)-based block copolymers for biomedical applications

Abstract: Nanostructure fabrication from block copolymers is discussed in this review paper. Particularly, novel approaches for the construction of functionalized poly(ethylene glycol) (PEG) layers on surfaces were focused to attain the specific adsorption of a target protein through PEG-conjugated ligands with a minimal non-specific adsorption of other proteins. Furthermore, surface organization of block copolymer micelles with cross-linking cores was described from the standpoint of preparation of a new functional surface-coating with a unique macromolecular architecture. The micelle-attached surface and the thin hydrogel layer made by layered micelles exhibited non-fouling properties and worked as a reservoir for hydrophobic reagents. These PEG-functionalized surface in brush form or in micelle form can be used in diverse fields of medicine and biology to construct high-performance medical devices including scaffolds for tissue engineering and matrices for drug delivery systems.

A novel LIESST iron(II) complex exhibiting a high relaxation temperature.

Abstract: The spin-crossover iron(II) complex [Fe(L)(CN)2]·H2O (1) has been investigated. Complex 1 has a pentagonal bipyramidal structure which is seven-coordinated, containing an N3O2 macrocycle and two CN- ligands. Water molecules bind the complex by means of hydrogen bonding. It was found that the complex 1 exhibited a light-induced excited spin state trapping (LIESST) effect. The relaxation temperature is above 130 K, which is the highest temperature for LIESST compounds reported so far.

Measurement of adhesive force between mold and photo-curable resin in imprint technology

Abstract: Imprint lithography using photocurable resin is the most promising technique compared with other imprint lithography techniques, because it can complete a pattern transfer at room temperature. Thus, it would be able to implement practical mass-production lithography. In a previous report, however, a part of the solidified polymer was ripped away, because of strong adhesive force between the mold and solidified polymer. In order to improve this phenomenon, release coating of quartz mold and development of a photocurable resin are necessary. In this paper, we describe a measurement method of adhesive force between mold and resin using a tensile tester and, furthermore, durability of release coating material.

Analysis of Aldehydes in Water by Head Space-GC/MS

Abstract: The concentrations of formaldehyde, acetaldehyde, propionaldehyde, and n-butyraldehyde in water were quantitatively determined by head space-gas chromatography/mass spectrometry (HS-GC/MS). Aqueous aldehydes were treated with o-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine (PFBOA) in a sealed vial at 60°C for 60 min. Head space was then analyzed by GC/MS. In comparison with electron ionization (EI) mass spectra, negative chemical ionization (NCI) mass spectra of PFBOA derivatives gave more spectral peaks of structural origin and with simple, characteristic fragmentation patterns. HS-GC/MS is highly sensitive for aqueous aldehydes because it eliminates interference from the water sample. The concentrations of various aldehydes in tap water and commercial mineral water were determined by HS-GC/MS. The following concentration ranges were detected for the individual aldehydes; formaldehyde, not detected (N.D.)-59 µg/l; acetaldehyde, N.D.-260 µg/l; propionaldehyde, N.D.- 0.9 µg/l; and n-butyraldehyde, N.D-0.3 µg/l.

Localized exciton dynamics in strained cubic In0.1Ga0.9N/GaN multiple quantum wells

Abstract: Radiative and nonradiative recombination dynamics in strained cubic (c-) In0.1Ga0.9N/c-GaN multiple quantum wells were studied using temperature-dependent time-resolved photoluminescence (TRPL) spectroscopy. In contrast to hexagonal InGaN quantum wells, low-excitation photoluminescence peak energy increased moderately with decreasing well thickness L and the PL lifetime did not strongly depend on L. The results clearly indicated that the piezoelectric field was not acting on the transition process. The TRPL signal was well fitted as a stretched exponential decay from 10 to 300 K, showing that the spontaneous emission is due to the radiative recombination of excitons localized in disordered quantum nanostructures such as In clusters. The localized states were considered to have two-dimensional density of states at 300 K (quantum disk size), since the radiative lifetime increased with increasing temperature above 150 K.

Optical and structural studies in InGaN quantum well structure laser diodes

Abstract: An InGaN multiple-quantum-well laser diode wafer that lased at around 400 nm was shown to have the InN mole fraction, x, of only 6% in the wells. Nanometer-probe compositional analysis showed that the fluctuation of x was as small as 1% or less, which is the resolution limit. However, the wells exhibited a Stokes-like shift (SS) of 49 meV at 300 K, which was approximately 65% of the luminescence linewidth, and effective localization depth, E0, was estimated to be 35 meV at 300 K. Since the effective electric field due to polarization in the wells was estimated to be as small as 300 kV/cm, SS was considered to originate from effective band-gap inhomogeneity. Because the well thickness fluctuation was insufficient to reproduce SS or E0 and bulk cubic In0.02Ga0.98N that does not suffer any polarization field or thickness fluctuation effect exhibited a SS of 140 meV at 77 K, the exciton localization is considered to be an intrinsic phenomenon in InGaN, which is due to the large band-gap bowing and In clusteri...

Asymmetric autocatalysis and the origin of chiral homogeneity in organic compounds

Abstract: The discovery and development of asymmetric autocatalysis, in which the structures of the chiral catalyst and the chiral product are the same, are described. Chiral 5-pyrimidyl, 3-quinolyl, and 5-carbamoyl-3-pyridyl alkanols act as highly enantioselective asymmetric autocatalysts in the enantioselective addition of diisopropylzinc to the corresponding aldehydes, such as pyrimidine-5-carbaldehyde. 2-Alkynyl-5-pyrimidyl alkanol with an enantiomeric excess (ee) of >99.5% automultiplies practically perfectly as an asymmetric autocatalyst in a yield of >99% and >99.5% ee. Asymmetric autocatalysis with an amplification of ee has thus been realized. Consecutive asymmetric autocatalysis starting with chiral 2-alkynylpyrimidyl alkanol of only 0.6% ee amplifies its ee significantly, and yields itself as the product with >99.5% ee. The reaction of pyrimidine-5-carbaldehyde and diisopropylzinc in the presence of chiral initiators with low ee’s, such as secondary alcohol, amine, carboxylic acid, mono-substituted [2.2]paracyclophane, and chiral primary alcohols due to deuterium substitution, regulates the absolute configuration of the resulting pyrimidyl alkanols, and the ee of the resulting pyrimidyl alkanol is much higher than that of the chiral initiator. Leucine and [6]helicene with very low ee’s, which are known to be induced by circularly polarized light (CPL), also serve as chiral initiators to produce pyrimidyl alkanol with higher ee’s. Overall, the process represents the first correlation between the chirality of CPL and an organic compound with very high ee. Chiral inorganic crystals, such as quartz and sodium chlorate, act as chiral inducers in the asymmetric autocatalysis of pyrimidyl alkanol. The process correlates for the first time ever the chirality of inorganic crystals with an organic compound with very high ee. © 2001 John Wiley & Sons, Inc. and The Japan Chemical Journal Forum Chem Rec 1:321–332, 2001

Oscillator representations and systems of ordinary differential equations

Abstract: Using representation-theoretic methods, we determine the spectrum of the 2 x 2 system. Q(x, D(x)) = A- partial differential(2)(x)2 + x(2)2 + Bx partial differential(x) + 1/2, x in, with A, B in Mat(2)(R) constant matrices such that A = (t)A > 0 (or <0), B = -(t)B not equal 0, and the Hermitian matrix A + iB positive (or negative) definite. We also give results that generalize (in a possible direction) the main construction.

Impact of growth polar direction on the optical properties of GaN grown by metalorganic vapor phase epitaxy

Abstract: The growth polar direction during metalorganic vapor phase epitaxy of wurtzite GaN was shown to affect the optical properties in terms of impurity and vacancy incorporation during the growth. The GaN film grown toward the Ga (0001) face (+c polarity) exhibited clear excitonic features in its optical absorption and luminescence spectra up to room temperature. Conversely, the film with the N (0001) face (−c polarity) exhibited a broad emission band, which locates in the broad absorption tail. The difference between the two was explained in terms of the presence of impurity-induced band-tail states in −c GaN due to increased impurity density and incorporation of large volume vacancy-type defects, which were confirmed by secondary ion mass spectrometry [Sumiya et al., Appl. Phys. Lett. 76, 2098 (2000)] and monoenergetic slow positron annihilation technique.

Low-density parity-check (LDPC) coded OFDM systems

Abstract: Orthogonal frequency division multiplexing (OFDM) is a very attractive technique for high-bit-rate data transmission in a multipath fading environment that causes intersymbol interference (ISI). There are many error-correcting codes applied to OFDM, convolutional codes, Reed-Solomon codes, turbo codes, and so on. Low-density parity-check (LDPC) codes have attracted much attention particularly in the field of coding theory. LDPC codes were proposed by Gallager (1962) and the performance is very close to the Shannon limit with practical decoding complexity like turbo codes. We propose LDPC coded OFDM (LDPC-COFDM) systems to improve the bit error rate (BER) of OFDM. We show that the BER of the LDPC-COFDM is worse than that of the TCOFDM on an AWGN channel, while that of the LDPC-COFDM is better than that of the turbo-coded OFDM (TCOFDM) on a frequency-selective fading channel.

Structure of alkanethiolate monolayers on Cu(100): Self-assembly on the four-fold-symmetry surface

Abstract: We have studied the structure and growth process of hexanethiolate self-assembled monolayers (SAMs) on Cu( 100) by means of scanning tunneling microscopy (STM) and X-ray absorption fine structure (XAFS) spectroscopy. At saturated coverage, the thiolates are assembled into a c(2 x 6) structure with zigzag chains along the close-packed Cu rows. The sulfur atom of the thiolate occupies the 4-fold hollow site of the unreconstructed Cu(100) surface with a nearest-neighbor S-S distance of 3.6 A. Such sulfur adsorption results in a large lattice mismatch between the S/Cu layer and the alkyl chain layer, since the interchain distance of the alkyl group is ca. 4.5 A. However, it is reconciled by the internal degree of freedom for the S-C bond which bridges the two layers, as is confirmed by the geometrical optimization based on molecular force-field calculations. The SAM film formation is well-described by a two-step process; in the first step, a full-coverage monolayer is rapidly formed, which is characterized by a highly oriented but two-dimensionally disordered structure, followed by a much slower evolution to the c(2 x 6) structure with surface diffusion of the thiolate.

Uniformity in patterns imprinted using photo-curable liquid polymer

Abstract: Imprint lithography reported by Chou et al (Appl. Phys. Lett. vol. 67, p. 3114, 1995) may become one of the most promising lithographic technologies in terms of mass-production and low equipment cost . In particular, those based on photo-induced solidification (Haisma et al, 1996; Bailey et al, 2000) are very attractive because of elimination of heat-up and cool-down time and the possibility of a step and repeat procedure. We have already reported preliminary results (Komuro et al, Jpn. J. Appl. Phys., vol. 39, p. 7075, 2000) by imprint using liquid polymer curable by ultra-violet (UV) light exposure. The paper shows the pattern fabrication process by imprint using photo-curable liquid polymer. The base layer, which is accompanied with a press process, must be removed by etching. In this paper, we describe uniformity in imprinted patterns and reproducibility of our imprint process.

Protonic Conduction in the Single Crystals of SrZr0.95M0.05O3 (M=Y, Sc, Yb, Er)

Abstract: The protonic conductivities of SrZr0.95M0.05O3 doped with four acceptor ions (M3+=Y3+, Sc3+, Yb3+, Er3+) have been studied in the single crystal form. The protonic conductivity is found in four acceptor ions, indicating that protons migrate by hopping from site to site. The Yb-doped crystal has the lowest activation energy and the highest conductivity amongst the four acceptor ions. This is considered to be due to the difference in strength of the O–H bond with different acceptor doping.

Realistic facial expressions by SMA driven face robot

Abstract: The goal of this study is to investigate the intelligence of non-verbal communication taking place between an anthropomorphic agent and a human when the agent works together with human. For this purpose, it seems necessary to build an anthropomorphic robot as a test bed and/or platform that can recognize and express nonverbal messages. As faces and facial expressions are crucial for non-verbal communication, we have been developing a human-like robot face that can express facial expressions. The important factor of such a robot face is the realism of the face and facial expressions. We used air cylinders with pressurized air for the Mark I robot face, but now we have decided to use an SMA (shape memory alloy) actuators driven by electricity. In this paper, we present the prototype SMA-actuated robot face and show its capability of producing six kinds of realistic facial expression: surprise, fear, anger, disgust, sad and happy. Kansei evaluation of these facial expressions shows good expressiveness in the robotic facial expressions.

Fluid flow and mass transfer characteristics in a sinusoidal wavy-walled tube at moderate Reynolds numbers for steady flow

Abstract: Flow and mass transfer characteristics in an axisymmetric sinusoidal wavy-walled tube are investigated experimentally in the Reynolds number range from 50 to 1000. The flow patterns are visualized by the aluminum dust method. The measurements of the wall shear stress and the mass transfer rate for high Schmidt number are performed by the electrochemical method. The attention is focused on their characteristics, including the transitional flow. It was observed that steady flow changes into unsteady flow when the Reynolds number exceeds about 160. The wall shear stress in the minimum circular cross section of the tube and the mass transfer rate for one wavelength are shown to depend upon the Reynolds number. In the laminar flow regime they increase with the slope of 1 and 1/3, respectively, whereas in the turbulent flow regime they increase with the slope of 3/2 and 3/5, respectively. In the transitional flow regime both of them increase significantly with further larger slope. It is found that the laminar-like motion and turbulent-like motion occur alternatively, with different time intervals, indicating intermittent flow behavior. This is quite different from the flow instability of the wavy-walled channel in which Tollmien-Schlichting waves keeping a time-periodic flow appear.

Monoester Formation by Hydrolysis of Dialkyl Phthalate Migrating from Polyvinyl Chloride Products in Human Saliva

Abstract: The migration dialkyl phthalate was tested in volunteers who chewed polyvinyl chloride (PVC) toy products under controlled conditions. The PVC toy samples consisted of ball A containing 100 and 185 mg/ g di-n-butyl phthalate (DBP) and di-2-ethylhexyl phthalate (DEHP) respectively, and ball B, containing 256 mg/g diisononyl phthalate (DINP). The migration of dialkyl phthalate into simulated saliva was also tested in vitro by shaking toy samples. The migration rates of DBP, DEHP and DINP from balls A and B were 11.7, 44.4 and 78.0 µg/10 cm 2 /hr, respectively, in vivo, and 339, 315 and 535 µg/10 cm 2 /hr, respectively, in vitro. The presence of mono-n-butyl phthalate (MBP) and mono-2-ethylhexyl phthalate (MEHP) in saliva collected after chewing ball A was confirmed by GCMSSIM. Human saliva which collected from volunteers incubated with DBP and DEHP at 37°C over 60 min, hydrolyzed these compounds to their monoesters.

A Catalytic and Stereoselective Glycosylation with Glucopyranosyl Fluoride by Using Various Protic Acids

Abstract: A catalytic and stereoselective glycosylation with glucosyl fluoride was effectively performed by using a catalytic amount of various protic acids. When the glycosylation was carried out, for example, using perchloric acid (HClO4) in diethyl ether (Et2O), the major products were α-glycosides while β-stereoselectivity was observed when tetrakis(pentafluorophenyl)boric acid [HB(C6F5)4] was used in a mixed solvent of trifluoromethylbenzene (BTF)–pivalonitrile (tBuCN) = (5:1). The stereoselectivity was controlled by not only the effect of solvent but also by the nature of counter anion of the catalyst such as B(C6F5)4− or ClO4−.

Coulomb blockade in multiwalled carbon nanotube island with nanotube leads

Abstract: We propose and demonstrate a technique to form an ultrasmall island for a single-electron transistor in a multiwalled carbon nanotube (MWNT). The two small areas in the MWNT connected to electrodes were etched in oxygen plasma, resulting in the cutting of the MWNT into three pieces. An island and two leads connected the island through the tunneling barriers were made of the MWNT. In this device, we observed the Coulomb blockade effect at 4.5 K, and the estimated charging energy was 38 meV. This result is an essential step for the use of carbon nanotubes in nanoscale electronics circuits.

An Effective Method for the Preparation of Chiral Polyoxy 8-Membered Ring Enone Corresponding to the B Ring of Taxol

Abstract: An effective method for the preparation of 8-membered ring enone, (4S,5R,7R,8R)-4,8-bis(benzyloxy)-7-(t-butyldimethylsiloxy)-5-(4-methoxybenzyloxy)-2,6,6-trimethylcyclooct-2-enone (1), in sufficien...

Cation Distribution and Helimagnetic Structure of the Ba2(Zn1-xMgx)2Fe12O22 System as Revealed by Magnetization Measurements and Neutron Diffraction

Abstract: Magnetization measurements and neutron diffraction experiments were carried out on single crystals of Ba 2 (Zn 1- x Mg x ) 2 Fe 12 O 22 , where x is the Mg concentration ranging from x =0 to 1.0. T...